Conventionally, an exhaust gas turbine supercharger and compressor housing described in, for example, Patent Document 1 are known as examples of the aforementioned types of exhaust gas turbine supercharger and compressor housing. The compressor housing (3) described in Patent Document 1 encloses an impeller (7) and includes an inlet portion (17), through which air is introduced toward the impeller (7). A bypass passage (27), which bypasses the impeller (7), is formed in the compressor housing (3). An air bypass mechanism (31) having a valve body for selectively opening and closing the bypass passage (27) is arranged in the bypass passage (27). A port portion, against which the valve body can rest, is arranged adjacent to the inlet portion (17).
In the exhaust gas turbine supercharger, the supply of air toward the impeller through the inlet portion is suspended when, for example, the accelerator is deactivated. This moves the valve body of the air bypass mechanism to an open position, thus returning some of the air from the downstream side to the upstream side with respect to the impeller. As a result, surging is avoided.